Fix a number of outstanding issues:

* {{}} escape their contents, {{{}}} and {{& }} do not
* Add support in the parser, tokenizer and AST for partials
  with context (support is still not there in the runtime)
* Fix some inconsistencies with the old behavior involving
  the correct printing of null and undefined
* Add Handlebars.Exception
* Fixed an issue involving ./foo and this/foo
* Fleshed out helperMissing in the specs (this will be
  moved out into handlebars proper once registerHelper
  and registerPartial are added)

spec/spec_helper.rb

@@ -40,6 +40,7 @@ module Handlebars
       context.load('lib/handlebars/printer.js')
       context.load('lib/handlebars/parser.js')
       context.load('lib/handlebars/runtime.js')
+      context.load('lib/handlebars/utils.js')
       context.load('lib/handlebars.js')
     end
   end